Heretofore, it has been well known to have keyboard assemblies which includes switches on a printed circuit board consisting of dome-shaped resilient elements coacting with contacts at switch sites on the board where depression and tripping of a dome-shaped element causes actuation of the switch at the switch site of the element. While the switch is normally open, depressing of the dome-shaped resilient element and tripping of same causes the switch to close.
Typical dome-shaped resilient elements on a printed circuit board are illustrated in U.S. Pat. No. 3,967,084. Such elements have been called click springs, dome springs, snap dome switches, and quite often just domes. It is advantageous to use a dome because when depressed and actuated it produces a tactile feedback or snap action upon being tripped that is felt by the user to indicate switch closing action. These domes are in effect electrically conductive spring members which, when depressed and tripped and further depressed by a lesser force, will bridge contacts to close one or more electrical circuits. A spring return force is generated upon tripping which upon release of the depressing force causes the dome to return to its original form to open the contacts. The tactile feedback is considered the difference between the trip force and the release force.
Domes have been known to be of different shapes but usually are circular in form, such as disclosed in U.S. Pat. No. 3,967,084. An example of polygonally shaped domes is shown in U.S. Pat. No. 4,071,718. Further, domes have been formed with feet such as illustrated in U.S. Pat. No. 3,967,084.
Heretofore, the life of keyboard assemblies depends primarily upon the life of the domes. Failure of the domes has been encountered where they have been subjected to a number of tripping cycles. While the life expectancy heretofore may be extended in certain domes, it is done only at the sacrifice of tactile feel. Likewise, when better tactile feel is desired and built into a doom, life expectancy of the dome is sacrificed. Thus, heretofore it was possible only to obtain in domes either a desired life expectancy or a desired tactile feel. Another problem encountered with heretofore known domes is that they have been corner sensitive where, when an actuator button aligned with the dome is hit or pushed on its corner, it would not reliably make contact with all of the contacts.